478 BONES OF SHOULDER I SCAPULA AND CLAVICLE. 



firmer attachment to the muscles that arise from it (fig. 226, 3 ). 

 The scapula is never deficient in animals that possess a superior 

 extremity, though sometimes it is very narrow. The muscles 

 attached to it are chiefly those which draw the arm upwards, 

 and which turn it on its axis. In Man, their actions are 

 very numerous and varied ; but in animals that only use 

 their extremities for giving motion to the body, the muscular 

 apparatus is much simpler, and the scapula is narrower (fig. 

 229, o). This is particularly the case in Birds (fig. 250, o), 

 the raising of whose wings in flight is an action that requires 

 very little power, though for their depression or pulling-down 

 great muscular force is needed. 



636. The Clavicle is a rounded bone, attached at one ex- 

 tremity to the acromion-process of the scapula, and at the 

 other to the top of the sternum. Its principal use is to keep 

 the shoulders separate ; and we accordingly find it strongest 

 in those animals, the actions of whose superior extremities 

 tend to draw them together ; whilst it is comparatively weak 

 or altogether deficient in animals, the actions of whose limbs 

 naturally tend to keep them asunder. In Birds, the violent 

 drawing-down of whose wings in flight would tend to bring 

 the shoulders together if they were not prevented, there is 

 not only a strong clavicle, but usually a second bone having 

 a similar function ( 668). In the Horse and other animals, 

 on the contrary, the bearing of whose weight on their fore- 

 legs tends rather to separate the shoulders than to bring them 

 together, the clavicle is deficient. 



637. The Scapula is connected with the central framework 

 of the skeleton by various muscles (fig. 226), which pass 

 towards it from the spinal column and ribs, and which serve 

 alike to fix it, and to assist in sustaining the weight which it 

 sometimes has to bear. In Man these are numerous, and their 

 actions are various ; since the scapula is left very movable in 

 him, that the actions of the arm may be more free. In 

 Quadrupeds it is generally more fixed ; and the trunk is slung 

 from it, as it were, by a muscle (the serratus magnus, 9 ) of mode- 

 rate thickness in Man, but in these animals of great strength, 

 which passes from the scapula to be attached to the ribs. 



638. The superior or anterior member itself is divided into 

 three principal portions, the arm, fore-arm, and hand. The 

 arm is supported by a single long and cylindrical bone, which 



